This invention relates to an electro-optical web inspection system for detecting and extracting oversize hole, clump or color related web defect signals from a noisy product scan signal. More particularly, it is concerned with auxiliary apparatus for continuously self-checking the operation of the system to determine when it fails to detect defects of predescribed character. The auxiliary equipment which comprises this invention is attached to the flying spot inspection system of U.S. Pat. No. 3,866,054 which is assigned to the assignee of this application.
The web inspection system of the above-referenced patent operates satisfactorily. However, significant expenditures of time and effort has been required in order to calibrate the discriminator circuits for proper sensitivity and to periodically check that prescribed discriminator circuit threshold levels are being maintained and proper gates are being generated.